Editing Fluorescent lamp (section)

===Cold-cathode fluorescent lamps===  <!-- target of redirect -->
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{{Further|Cold cathode}}
[[File:Cold Cathode Fluorescent Lamp.JPG|thumb|A cold-cathode fluorescent lamp from an emergency-exit sign. Operating at a much higher voltage than other fluorescents, the lamp produces a low-amperage [[glow discharge]] rather than an arc, similar to a [[neon light]]. Without direct connection to line voltage, current is limited by the transformer alone, negating the need for a ballast.]]

Most fluorescent lamps use electrodes that emit electrons into the tube by heat, known as hot cathodes. However, [[cold cathode]]  tubes have cathodes that emit electrons only due to the large [[voltage]] between the electrodes. The cathodes will be warmed by current flowing through them, but are not hot enough for significant [[thermionic emission]]. Because cold cathode lamps have no thermionic emission coating to wear out, they can have much longer lives than [[hot cathode]] tubes. This makes them desirable for long-life applications (such as backlights in [[liquid crystal display]]s). Sputtering of the electrode may still occur, but electrodes can be shaped (e.g. into an internal cylinder) to capture most of the sputtered material so it is not lost from the electrode.

Cold cathode lamps are generally less efficient than thermionic emission lamps because the cathode fall voltage is much higher. Power dissipated due to cathode fall voltage does not contribute to light output. However, this is less significant with longer tubes. The increased power dissipation at tube ends also usually means cold cathode tubes have to be run at a lower loading than their thermionic emission equivalents. Given the higher tube voltage required anyway, these tubes can easily be made long, and even run as series strings. They are better suited for bending into special shapes for lettering and signage, and can also be instantly switched on or off.